The present invention relates to internal-combustion engines of the type with at least two inlet valves for each cylinder and an electronically controlled hydraulic system for variable actuation of the inlet valves.
The present applicant has already proposed in the U.S. Pat. No. 6,237,551 an engine comprising:
at least two inlet valves for each cylinder, each provided with respective elastic-return means, which push the valve towards a closed position, for controlling respective induction and exhaust ducts;
at least one camshaft for actuating each inlet valve of the cylinders of the engine by means of respective tappets, each inlet valve being controlled by a respective cam of said camshaft,
in which each of said tappets controls the respective inlet valve against the action of said elastic-return means by the interposition of hydraulic means, which include a pressurized fluid chamber,
the pressurized fluid chamber associated to each inlet valve being designed for being connected by means of a solenoid valve to an -exhaust duct for the purpose of uncoupling the valve from the respective tappet and causing rapid closing of the valve as a result of the respective elastic-return means; and
electronic control means for controlling each solenoid valve for varying the time and stroke of opening of the respective inlet valve or exhaust valve according to one or more operating parameters of the engine.
The present applicant has also already proposed in the Italian patent application T02001A000660, dated Jul. 6, 2001 (still secret at the date of filing of the present patent application), an engine of the type specified above, in which the inlet valves associated to each cylinder are controlled in a differentiated way in time and/or in the extent of opening, so that a first inlet valve follows a first law of opening and closing, whilst a second inlet valve follows a second law of opening and closing.
Independently of the solution previously proposed, controlling in a differentiated way opening and closing of the two inlet valves of each cylinder may be useful for any other reason. Obviously, in the case of differentiated control, it follows that the parts of the system associated to the two inlet valves are subject to different stresses, which result in a substantial intrinsic asymmetry of the system.
The purpose of the present invention is to overcome the above drawback, guaranteeing a uniform stress on the systems for actuating the two inlet valves of each cylinder.
In order to achieve the above purpose, the subject of the invention is an engine which has all the characteristics referred to at the start and which is further characterized in that the two inlet valves associated to each cylinder are controlled in a differentiated way in time and/or in extent of opening, so that at each engine cycle an inlet valve follows a first law of opening and closing, whilst the other inlet valve follows a second law of opening and closing, and in that the aforesaid electronic control means are programmed for reversing with respect to one another the laws of opening and closing of the two inlet valves of the same cylinder with a periodicity equal to one or more engine cycles, so that each of the two inlet valves follows alternately the first law or the second law of opening and closing at each successive period.